Translocation of food in plants was demonstrated by

Step-by-step solution

A simple experiment, called girdling, was used to identify the tissues through which food is transported. On the trunk of a tree, a ring of bark up to a depth of the phloem layer can be carefully removed. In the absence of a downward movement of food, the portion of the bark above the ring on the stem becomes swollen after a few weeks. This simple experiment shows that phloem is the tissue responsible for translocation of food; and that transport takes place in one direction, i.e., towards the roots.